A general approach to the interpretation of electrochemical quartz crystal microbalance data

Overview and Recent Advances in Hyphenated Electrochemical Techniques for the Characterization of Electroactive Materials

A hyphenated electrochemical technique consists of the combination of the coupling of an electrochemical technique with a non-electrochemical technique, such as spectroscopical and optical techniques, electrogravimetric techniques, and electromechanical techniques, among others. This review highlights the development of the use of this kind of technique to appreciate the useful information which can be extracted for the characterization of electroactive materials. The use of time derivatives and the acquisition of simultaneous signals from different techniques allow extra information from the crossed derivative functions in the dc-regime to be obtained. This strategy has also been effectively used in the ac-regime, reaching valuable information about the kinetics of the electrochemical processes taking place. Among others, molar masses of exchanged species or apparent molar absorptivities at different wavelengths have been estimated, increasing the knowledge of the mechanisms for different electrode processes.

Theory for Solvent and Salt Transfer Accompanying Partial Redox Conversion of Electroactive Polymer Films under Permselective and Nonpermselective Conditions

A comprehensive thermodynamic model for solvent and salt transfer accompanying a partial redox conversion, i.e., conversion between any two oxidation levels, of an electroactive polymer (EAP) film is presented. We discuss two possible cases, namely, one-phase and two-phase behavior of an EAP film. An expression describing the extent of solvent transfer in these situations is presented. Salt transfer is characterized by the difference in permselectivity indices (Delta R(b,a)) between two oxidation levels of the EAP film. Delta R(b,a) represents the difference in co-ion (salt) exclusion properties of the EAP in the two different oxidation levels. Delta R(b,a) is expressed in terms of the EAP's charge, number of electrons transferred in the redox reaction of an electroactive unit, concentration of the supporting electrolyte, salt partition coefficient between solvent and EAP phases, and salt activity coefficients in both phases. Plots of Delta R(b,a) as a function of the electrolyte concentration allow determining the EAP's phase behavior, ratio of salt partition coefficients, and number of electrons exchanged in the redox process. Delta R(b,a) is an experimentally accessible quantity; it can be obtained from electrochemical quartz crystal microbalance (EQCM) experiments. Delta R(b,a) values can be used as a diagnostic tool to characterize an EAP film.